This application claims benefit of Japanese Application No. 2002-51812 filed on Feb. 27, 2002, in Japan, and No. 2002-51813 filed on Feb. 27, 2002, in Japan, the entire contents of both of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a lens barrel.
2. Description of the Related Art
A conventional lens barrel shown in a vertical sectional view in FIG. 10 has been known as a lens barrel having a cam frame which can be rotationally and linearly moved, and a lens frame which can be linearly driven by the cam frame. A conventional lens barrel 50 comprises, a fixed frame 51, a cam frame 52, a first group frame (described hereafter as the first group frame) 53 holding first group lenses 65, a second group frame (described hereafter as the second group frame) 54 which slidably supports a lens frame 59 holding second group lenses 66, a third group frame (described hereafter as the third group frame) 55 holding third group lenses 67, and a straight float key 56.
Note that, with the second group frame 54, shutter blades 68 are mounted thereto, and a blade suppressor 58, which is a suppression member for the shutter blades 68, is mounted thereto. A compression spring 57 is inserted between the blade suppressor 58 and the third group frame 55 for preventing linear movement play.
With the cam frame 52, a male helicoid 52a, which spirally meshes with a female helicoid 51a of the fixed frame 51, is provided on the outer circumference of the back end thereof, and furthermore, the female helicoid 52b and two pairs of cam grooves 52c and 52d are provided at the inner circumference portion thereof, and a bayonet groove 52h, which is an inner groove for holding the straight float key 56, are provided on the back end of the inner circumference portion thereof. Note that the female helicoid 52b and two pairs of the cam grooves 52c and 52d are disposed such that the helicoid and the cam grooves cross one another as shown in a development of the inner circumferential face of the cam frame in FIG. 11 which will be described later.
With the first group frame 53, a male helicoid 53a which spirally meshes with the female helicoid 52b of the cam frame 52 is provided on the outer circumference portion of the back end thereof. With the second group frame 54, a cam follower 62, which is freely slidably fitted into the cam groove 52d of the cam frame 52, is implanted (supported in a fixed manner) on the outer circumference portion thereof. With the third group frame 55, a cam follower 61 which is freely slidably fitted into the cam groove 52c of the cam frame 52 is implanted (supported in a fixed manner) on the outer circumference thereof. With the straight float key 56, a protruding straight key 56b which is freely slidably fitted into a straight guide groove 51b of the fixed frame 51, and a bayonet tab 56a which is freely slidably fitted into the bayonet groove 52h of the cam frame 52, are provided.
With the lens barrel 50 having a linear driving mechanism described above, upon the cam frame 52 being rotationally driven by the lens barrel linear driving unit, the cam frame 52 is linearly moved while rotating. The straight float key 56 is linearly moved along the direction of the optical axis O along with the rotationally moving cam frame 52 without rotational movement. The first group frame 53, the second group frame 54, and the third group frame 55 are linearly driven, respectively, according to the rotational movement and linear movement of the cam frame 52 with the rotational movement being restricted by the straight float key 56.
Detailed description will be further made regarding the configuration of the inner circumference portion of the cam frame 52 with reference to FIG. 11 through FIG. 13. FIG. 11 is a development which illustrates an inner circumference face of the cam frame, FIG. 12 is a sectional view taken along line XIIxe2x80x94XII of FIG. 11, and FIG. 13 is a diagram which illustrates the bayonet tab of the cam frame 52 and the insertion portion for the cam follower, as viewed from the back end side.
As shown in FIG. 11, with the inner circumference face of the cam frame 52, the female helicoid 52b with a predetermined lead, and three pairs of the cam grooves 52c and 52d are provided, and a bayonet groove 52h is provided at the back end face side. Furthermore, six notch-shaped inserting portions 52e for inserting the bayonet tab 56a, and three notch-shaped inserting portions 52f and 52g for inserting the cam followers 61 and 62, are provided on a ring-shaped back end wall portion 52j on the back end face where the bayonet groove 52h of the cam frame 52 is provided, respectively, as shown in FIG. 13. The cam followers 61 and 62 are fitted into the cam grooves 52c and 52d through the inserting portions 52f and 52g. The bayonet tab 56a is fitted into the bayonet groove 52h through the inserting portion 52e. Note that the inner diameter of the inner circumference face 52i (see FIG. 13) of the cam frame 52 is the same as the inner diameter of the back end wall portion 52j. 
The female helicoid 52b of the cam frame 52 has a thread height (depth) H0 from the inner circumference face 52i. The male helicoid 53a of the first group frame 53 which spirally meshes with the female helicoid 52b also has the same thread height (depth) H0. The cam grooves 52c and 52d of the cam frame 52 have a groove depth C0 from the inner circumference face 52i. The minimal wall thickness of the circumference portion of the cam frame 52 is represented by t0. The thickness d0 from the outer circumference face up to the inner circumference face 52i where the cam grooves are provided is C0+t0.
The total wall thickness (required frame thickness) T0 of the cam frame 52 in the radial direction is a thickness wherein the thread height H0 of the female helicoid 52b and the thickness d0 from the outer circumference face up to the inner circumference face 52i of the cam groove are added. That is to say, the total wall thickness T0 in the radial direction T0 is represented by
T0=H0+d0.
Substituting the above-described d0=C0+t0, the following expression is obtained.
T0=H0+C0+t0xe2x80x83xe2x80x83(1)
Note that a zoom lens barrel according to conventional art has been disclosed in Japanese Unexamined Patent Application Publication No. 6-67076, which employs a linear driving mechanism wherein the helicoid and the cam groove are disposed on the inner circumference face of the cam frame so as to cross one another, as with the conventional lens barrel shown in FIG. 10 described above.
With the above-described conventional lens barrel 50 shown in FIG. 10, while the cam grooves 52c and 52d, and the female helicoid 52b are disposed so as to cross one another, these are disposed in a pattern separated one from another. Accordingly, the total wall thickness (required frame thickness) T0 in the radial direction of the cam frame 52 with the minimal wall thickness t0 is obtained by simply adding the thread height H0 and the thickness d0 up to the outer face from the inner face.
A lens barrel according to the present invention comprises a first frame and a second frame. With the first frame, a first female helicoid is formed on the first region on the inner circumference face thereof, and a second female helicoid is formed with the same lead as the first female helicoid and a different groove depth from that of the first female helicoid on the second region in the inner circumference face thereof. The second frame is disposed inside of the first frame, and a first male helicoid which spirally meshes with the first female helicoid, and a second male helicoid which spirally meshes with the second female helicoids, are formed on the outer circumference thereof. The second frame is relatively rotated with respect to the first frame so as to be linearly driven.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereafter.